NAME
Hash::Ordered - A compact, pure-Perl ordered hash class
VERSION
version 0.001
SYNOPSIS
use Hash::Ordered;
my $oh = Hash::Ordered->new( a => 1 );
$oh->get( 'a' );
$oh->set( 'a' => 2 );
$oh->exists( 'a' );
$val = $oh->delete( 'a' );
@keys = $oh->keys;
@vals = $oh->values;
@pairs = $oh->as_list
$oh->push( c => 3, d => 4 );
$oh->unshift( e => 5, f => 6 );
( $k, $v ) = $oh->pop;
( $k, $v ) = $oh->shift;
$iter = $oh->iterator;
while( ( $k, $v ) = $iter->() ) { ... }
$copy = $oh->clone;
$subset = $oh->clone( qw/c d/ );
$reversed = $oh->clone( reverse $oh->keys );
@value_slice = $oh->values( qw/c f/ ); # qw/3 6/
@pairs_slice = $oh->as_list( qw/f e/ ); # qw/f 6 e 5/
DESCRIPTION
This module implements an ordered hash, meaning that it associates keys
with values like a Perl hash, but keeps the keys in a consistent order.
Because it is implemented as an object and manipulated with method
calls, it is much slower than a Perl hash. This is the cost of keeping
order.
METHODS
new
$oh = Hash::Ordered->new;
$oh = Hash::Ordered->new( @pairs );
Constructs an object, with an optional list of key-value pairs.
clone
$oh2 = $oh->clone;
$oh2 = $oh->clone( @keys );
Creates a shallow copy of an ordered hash object. If no arguments are
given, it produces an exact copy. If a list of keys is given, the new
object includes only those keys in the given order. Keys that aren't in
the original will have the value "undef".
keys
@keys = $oh->keys;
Returns the ordered list of keys.
values
@values = $oh->values;
@values = $oh->values( @keys );
Returns an ordered list of values. If no arguments are given, returns
the ordered values of the entire hash. If a list of keys is given,
returns values in order corresponding to those keys. If a key does not
exist, "undef" will be returned for that value.
get
$value = $oh->get("some key");
Returns the value associated with the key.
set
$oh->set("some key" => "some value");
Associates a value with a key and returns the value. If the key does not
already exist in the hash, it will be added at the end.
exists
if ( $oh->exists("some key") ) { ... }
Test if some key exists in the hash (without creating it).
delete
$value = $oh->delete("some key");
Removes a key-value pair from the hash and returns the value. This is
expensive, as the ordered list of keys has to be updated.
push
$oh->push( one => 1, two => 2);
Add a list of key-value pairs to the end of the ordered hash. If a key
already exists in the hash, it will be deleted and re-inserted at the
end with the new value.
Returns the number of keys after the push is complete.
pop
($key, $value) = $oh->pop;
Removes and returns the last key-value pair in the ordered hash.
unshift
$oh->unshift( one => 1, two => 2 );
Adds a list of key-value pairs to the beginning of the ordered hash. If
a key already exists, it will be deleted and re-inserted at the
beginning with the new value.
Returns the number of keys after the unshift is complete.
shift
($key, $value) = $oh->shift;
Removes and returns the first key-value pair in the ordered hash.
merge
$oh->merge( one => 1, two => 2 );
Merges a list of key-value pairs into the ordered hash. If a key already
exists, its value is replaced. Otherwise, the key-value pair is added at
the end of the hash.
as_list
@pairs = $oh->as_list;
@pairs = $oh->as_list( @keys );
Returns an ordered list of key-value pairs. If no arguments are given,
all pairs in the hash are returned. If a list of keys is given, the
returned list includes only those key-value pairs in the given order.
Keys that aren't in the original will have the value "undef".
iterator
$iter = $oh->iterator;
$iter = $oh->iterator( reverse $oh->keys ); # reverse
while ( my ($key,$value) = $iter->() ) { ... }
Returns a code reference that returns a single key-value pair (in order)
on each invocation, or the empty list if all keys are visited.
If no arguments are given, the iterator walks the entire hash in order.
If a list of keys is provided, the iterator walks the hash in that
order. Unknown keys will return "undef".
The list of keys to return is set when the iterator is generator. Keys
added later will not be returned. Delete keys will return "undef".
OVERLOADING
Boolean
if ( $oh ) { ... }
When used in boolean context, a Hash::Ordered object is true if it has
any entries and false otherwise.
MOTIVATION
For a long time, I used Tie::IxHash for ordered hashes, but I grew
frustrated with things it lacked, like a cheap way to copy an IxHash
object or a convenient iterator when not using the tied interface. As I
looked at its implementation, it seemed more complex than I though it
needed, with an extra level of indirection that slows data access.
Given that frustration, I started experimenting with the simplest thing
I thought could work for an ordered hash.
As I worked on this, I also started searching for other modules doing
similar things. What I found fell broadly into two camps: modules based
on tie (even if they offered an OO interface), and pure OO modules. They
all either lacked features I deemed necessary or else seemed overly
complex in either implementation or API.
Hash::Ordered attempts to find the sweet spot with simple
implementation, reasonably good efficiency for most common operations,
and a rich, intuitive API.
SEE ALSO
Tie modules
The following modules offer some sort of tie interface. I don't like
ties, in general, because of the extra indirection involved over a
direct method call, but if that doesn't bother you, you might want to
try one of these
Tie::IxHash is probably the most well known and includes an OO API. If
its warts and performance profile aren't a problem, it might serve.
Tie::LLHash I haven't used, but the linked-list implementation might be
worthwhile if you expect to do a lot of deletions.
Tie::Hash::Indexed is implemented in XS and thus seems promising if
pure-Perl isn't a criterion, but last I looked, it had a lot of CPAN
Testers failures, which lowers my trust in it.
These other modules have very specific designs/limitations and I didn't
find any of them suitable for general purpose use:
* Tie::Array::AsHash — array elements split with separator; tie API
only
* Tie::Hash::Array — ordered alphabetically; tie API only
* Tie::InsertOrderHash — ordered by insertion; tie API only
* Tie::StoredOrderHash — ordered by last update; tie API only
Other ordered hash modules
Other modules stick with an object-oriented API, with a wide variety of
implementation approaches.
Array::AsHash is essentially an inverse implementation from
Hash::Ordered. It keeps pairs in an array and uses a hash to index into
the array. I think this indirection makes hash-like operations slower,
but getting the list of pairs back out is much faster. It takes an
arrayref to initialize, but can shallow copy it if needed. I think this
is a reasonable alternative if static construction and listing out
contents is more common than individual item access.
These other modules have restrictions or particularly complicated
implementations (often relying on "tie") and thus I didn't think any of
them suitable for general purpose use:
* Array::Assign — arrays with named access; restricted keys
* Array::OrdHash — overloads array/hash deref and uses internal tied
data
* Data::Pairs — array of key-value hashrefs; allows duplicate keys
* Data::OMap — array of key-value hashrefs; no duplicate keys
* Data::XHash — blessed, tied hashref with doubly-linked-list
SUPPORT
Bugs / Feature Requests
Please report any bugs or feature requests through the issue tracker at
. You will be notified
automatically of any progress on your issue.
Source Code
This is open source software. The code repository is available for
public review and contribution under the terms of the license.
git clone https://github.com/dagolden/Hash-Ordered.git
AUTHOR
David Golden
COPYRIGHT AND LICENSE
This software is Copyright (c) 2014 by David Golden.
This is free software, licensed under:
The Apache License, Version 2.0, January 2004